Every pipe fitting has a specific job. Understanding what each type does — and when to use which — is fundamental to reading a piping isometric, placing a correct order, or building out a system in the field. Here’s a complete reference for the fitting types you’ll encounter most often.
Elbows
Elbows change the direction of flow. The two key variables are the angle and the radius.
90° Long Radius (LR) Elbow
The most common elbow. The centerline radius is 1.5x the nominal pipe size (1.5D). Smooth flow path with lower pressure drop. Standard for most process and industrial piping per ASME B16.9.
90° Short Radius (SR) Elbow
Centerline radius equals the nominal pipe size (1D). More compact than long radius but higher pressure drop. Used where space is tight. Less common — specify SR explicitly when needed.
45° Elbow
Changes direction 45 degrees. Long radius standard (1.5D). Used to offset pipe runs, connect diagonal branches, and route pipe around obstructions. Lower pressure drop than a 90° due to shallower turn.
180° Return Bend
A U-turn fitting that reverses flow direction completely. Used in heat exchangers, coils, and wherever pipe must double back on itself. Available in long and short radius.
Tees
Tees split or combine flow. They’re specified by three dimensions: run x run x branch.
Straight Tee
All three openings are the same size. Splits flow equally or combines two lines into one. The default when the spec just says “tee” without further qualification.
Reducing Tee
The branch outlet is smaller than the run. Specified as run x run x branch (e.g., 4" x 4" x 2"). Used when the branch line is a smaller size than the main run.
Reducers
Reducers transition between two pipe sizes. The two types differ in how they’re oriented:
Concentric Reducer
Both ends share the same centerline. Installed in vertical pipe runs to maintain alignment. Creates turbulence in horizontal liquid lines because air pockets can form at the top of the larger end.
Eccentric Reducer
One side is flat (flat side up in horizontal liquid lines). Prevents air accumulation and vapor lock in liquid service. Also used at pump suctions where equal elevation at the bottom of the pipe is needed. Flat side down in gas service.
Caps and Closures
Pipe Cap
Closes the end of a pipe. Butt weld cap installs over the beveled pipe end. Threaded cap screws onto a male-threaded pipe end. Used for permanent or temporary terminations, future tie-in points, and pressure testing.
Plug
Threaded male plug closes a female-threaded fitting or valve port. Available in hex head (wrench tightened) and square head. Used to block unused ports, branch connections, and instrument taps.
Couplings and Unions
Full Coupling
Connects two pieces of pipe end to end. Available in socket weld and threaded. Used to join pipe sections, extend a run, or repair a damaged section.
Half Coupling
One socket weld or threaded end only. Welded to the side of a pipe to create a branch connection. Also used as a nozzle on pressure vessels and tanks.
Reducing Coupling
Connects two different pipe sizes end to end. An alternative to using a full reducer when the transition is in a straight run of small-bore pipe.
Union
Three-piece fitting (two end fittings and a nut) that allows the joint to be disconnected without cutting pipe. Used where equipment needs to be removed for maintenance — pumps, filters, meters, valves.
Bushings
Bushings reduce from a larger to a smaller thread size within a single fitting. A hex bushing (or reducing bushing) has a male thread on the outside and female thread on the inside — it installs into a larger female port and accepts a smaller male fitting. Used extensively to reduce valve ports, manifolds, and instrument connections without using a full reducer fitting.
Quick Reference — Fitting Type by Application
| Need to… | Use This Fitting |
|---|---|
| Change direction 90° | 90° LR elbow (standard) or 90° SR elbow (tight space) |
| Change direction 45° | 45° elbow |
| Add a branch the same size as the run | Straight tee |
| Add a smaller branch off the main run | Reducing tee or half coupling + weld |
| Transition between pipe sizes (horizontal liquid) | Eccentric reducer, flat side up |
| Transition between pipe sizes (vertical or gas) | Concentric reducer |
| Close the end of a pipe permanently | Cap (butt weld or threaded) |
| Block an unused port or branch | Threaded plug |
| Join two pipe sections end to end | Coupling |
| Allow disconnection without cutting pipe | Union |
| Reduce thread size at a port | Hex bushing |
All Fitting Types in Stock at PVFPro
Elbows, tees, reducers, couplings, caps, and bushings in carbon steel, stainless, brass, copper, and black iron. In stock and ready to ship.
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